Gordon Brown came under pressure yesterday to impose a British arms embargo on Israel in protest at its actions in Gaza, and to call on the EU to join the boycott.

The call was made by Nick Clegg, the Liberal Democrat leader, in an article in the Guardian, and represents the first serious political pressure on the prime minister to do more to condemn Israel.

Clegg accused Brown of sitting on his hands and speaking like an accountant about the crisis, remarks that were likely to deeply offend the prime minister.

Downing Street insists that Brown has been acting tirelessly behind the scenes alongside Tony Blair, now a Middle East envoy, and the French president, Nicolas Sarkozy, to secure a ceasefire that the Israeli government will accept, including an international force to police the tunnels reportedly taking weapons into Gaza. The Labour MP Richard Burden said that 100 parliamentarians had signed a letter condemning the attacks on Gaza.

But Clegg, ahead of an expected Commons statement on Monday by the foreign secretary, David Miliband, writes in the Guardian: "The EU is by far Israel's biggest export market, and by far the biggest donor to the Palestinians. It must immediately suspend the proposed new co-operation agreement with Israel until things change in Gaza, and apply tough conditions on any long-term assistance to the Palestinian community.

"Brown must also halt Britain's arms exports to Israel, and persuade our EU counterparts to do the same. The government's own figures show Britain is selling more and more weapons to Israel, despite the questions about the country's use of force. In 2007, our government approved £6m of arms exports. In 2008, it licensed sales 12 times as fast: £20m in the first three months alone.

"There is a strong case that, given the Gaza conflict, any military exports contravene EU licensing criteria. Reports, though denied, that Israel is using illegal cluster munitions and white phosphorus, should heighten our caution. I want an immediate suspension of all arms exports from the EU, but if that cannot be secured Brown must act unilaterally."

He wrote that it was intolerable that Brown, like Blair, was making UK policy subservient to the US and condemned what he described as "the aching silence" of the US president-elect, Barack Obama.